Method and apparatus for determining effective porosity



July 6, 9 E. o. MATTOCKS METHOD AND APPARATUS FOR DETERMINING EFFECTIVEPOROSITY Filed NOV.. 29 1940 J in W s H d m f H H 4 n n R0 E J W mm m QW w W 1% M W M mo 5 3 W m E M m a W N v w 9 v0 W H m 5 m m 2 1 V0 m M 3W W m QT N. k m. 9 2 m h wmwxumozbw mm W 0F Q22 8 w om mm 11 MEUIHEOEEs5ou 7 0k mm mm mm mm 8 Patented July 6, 1943 'METHOD AND APPARATUS FORDETERMIN- ING EFFECTIVE POROSITY I Elmer 0. Matt'ocks, Bartlesville,kla., asslgnor to Phillips Petroleum Company, a corporation of DelawareApplicatiomNovember 29, 1940, Serial No. 367,855

'7 Claims.

This invention relates to an improved method and apparatus fordetermining the effective porosity of various solids, such as formationcores and other porous materials.

In drilling a hydrocarbon oil or gas well, it is common practice toobtain cores of the formation above or in the zone where hydrocarbon oiland/or gas are found. Such cores are obtained by the general methodsemployed in coring and having been obtained, various tests are madethereon to ascertain the productive value of the formation representedby the cores. One of the important characteristics of the core is itspore spaces, as any hydrocarbon fluids that may be present incores arecontained in these spaces. The connected pore spaces are of primeimportance in recovering oil or gas from a reservoir because thehydrocarbon fluids flow through these pores to the well bore. Aknowledge of the size and extent of pore space is needed for determiningthe amounts of fluids which may be recovered from the reservoir and fordetermining the effects of water encroachment which is common inparticular reservoirs. A study of the cores aids in estimating properrates of withdrawal of fluid from the reservoir in order to obtain amaximum life for the producing oil wells and to recover the maximumamount of hydrocarbon fiuids at the most economical cost.

The ratio of the volume of connected pore "spaces to the total bulkvolume of a formation 'is generally termed effective porosity and iscommonly expressed as a percentage. The effectiveporosity of cores canbe obtained by any one of several ways now commonly employed. One

method is to place the core with mercury in an air-tight container anddraw a vacuum on the core by withdrawing mercury from the container.

This removes the air from the pores of the core.

' Before the volume of air thus withdrawn from the pores. can bemeasured, the pressure of that trapped air must be adjusted toatmospheric pressure. This requires the introduction again of mercuryinto the container. This mercury generally covers the core, and sincepore space in the core is under a vacuum, mercury will enter the poresduring the action of equalizing the pressure of, the trapped air toatmospheric conditions. The core cannot be used for additional testsunless the mercury is first removed from it. The removal of this mercuryis a hazardous procedure; hence, the cores are discarded after a singletest.

Porosity measurements are made generally on pieces cut from cores andthe test specimens are usually relatively uniform in size and shape. The

data thus obtained from small pieces of core are used as representativesamples of considerably larger sections. While this method has decidedlimitations, the results are generally representative and are usable foruniform or nearly uniform formations. In the case of formations, such aslimestones and dolomites where the porosity varies widely over thelength of the core, considerable error may result from using smallsections of the core as representative of the formation. In this type ofnon-uniform formation, porosity tests should be made on relativelylarger sections of the core. To accomplish this by the present knownmethods would require a large bulky piece of equipment which could notbe used with the same degree of accuracy in testing smaller pieces ofcore. 0

My invention permits the determination of effective porosities of large,as well as small sections of cores, using the same apparatus with aminimum of operating technique and with the same degree of accuracy. Thepractice of my invention does not impair individual cores in any manner,and it is possible to use the same core for purposes other than porositydetermination or to make any desired number of porosity tests.

This invention has for its primary object, the provision of an improvedmethod and apparatus for measuring volumes of a porous solid for thepurpose of determining the effective porosity of that solid.

Another object of this invention is to provide a method and apparatusfor determining the volume of connected pore spaces within the cores ofrock formation or other porous solids.

A still further object of this invention is to provide a method andapparatus for determining the effective porosity of both large and smallcores, using the same apparatus with a minimum of operating technique toobtain results with the same degree of accuracy and for making anynumber of porosity determinations without impairing the core for furthertest purposes.

These and additional objects and advantages will be apparent to personsskilled in the art by reference to the following description andanriexed drawing which is an elevation view of the apparatus of myinvention.

Referring to the drawing, an open-ended core container of any desiredsize is designated by numeral l. A holder or vice 2 has a plate 3 and isso constructed that by actuating a. screw 4, core container I makes anair-tight seal with plate 3 and communicates with valves 5 and 8, and apressure gauge 1 through an outlet 8. Valve 5 communicates with a valve9 and drying tube I8 Y through conduit I I for supplying air or anyother desired gas, and also with a valve I 2 and a deadweight tester(not shown) through a conduit I3. A conduit I4 connects valve 8 with awater mathe mercury reaches the top 01' burette I8, valves 7 nometer Ithrough a valve I8,'with a mercury manometer." which serves only as apressure relief device, with a calibrated burette I8 through a 3-wayvalve I8, and with a manifold or header Header also communicates with aplurality of expansion bottles 21, 28, 29, 38 and 3I of known volumethrough valves 32, 33, 34, 98 and 38, respectively. A mercury levelingbulb 31 connects with a burette I8 through a flexible conduit 38,

as allowed by a valve 39. A second mercury leveling bulb 48 connectswith mercury manometer 24 through a conduit H, as allowed by a pinchvalve 42. A pair of stands 43 support the I mercury leveling bulbs 31and 40., A core section 44 is indicated in core container I. For ease oioperation, it is desirable to choose core containers which are as nearthe size suitable for the core to be tested as possible.

The effective porosity of a core is theratio ,of.

the volume of connected pore spaces to thebulk volume of the core, asexpressed in the percent in the formula,

wherein V is the volume of the connected pore spaces, V1: is the bulkvolume of the core as defined by its external dimensions, and Va is thecombined volume of the nonporous materials and the nonconnected porespaces. It is obvious that Vp=Vb-Vn. The bulk volume of the core Vb maybe ascertained by any one of the usual methods. The combined volume ofthe nonporous materials and the nonconnected pore spaces Vn is obtainedby practicing my invention and the above equation is then solved to findthe percent eifective porosity Vp.

To determine the value of Vn for core 44, the core is deposited in corecontainer I, which'is placed in vice 2; and by operating screw 4, anairtight seal is made with'plate 3. Core container I is thus placed incommunication with outlet 8, valves 5 and 8, and gauge 1. Valve 8 isclosed, valve 5 is opened, valve I2 is closed, and air enters scorecontainer I through air supply Effective porosity i X 100= X 100 conduitII, drying tube III and valve 9. The air mitted into burette I8 byopening valve. When 39 and I9 are closed.- Valves 32, 33', 34, 35 and 38are then opened and the plurality of expansion bottles represented'by21, 28, 29, 38 and 3I are I connected into manifold 28. Vacuumpump 23 isthen connected into the system through conduit 28 and 3-way valve 23 isopened, thereby permitting manifold 28 and mercury manometer 24 tocommunicate with the vacuum pump 28. By positioning leveling bulb 48 sothat the open or atmospheric side of the manometer mospheric pressure,the zero point being on the closed side next to valve 23, it is possibleto read the absolute pressure in the expansion bottles. The pressure inthese bottles during evacuation is observed on manometer. 24. After thebottles are evacuated, valves 32, 33, 34, "and 38 are closed; vacuumpump 25 is disconnected from the system; and mercury manometer 24 isconnected into the manifold 20 by operating 3-way valve 23. Valves 2Iand 22 are then opened, adjusting the manifold 20 to atmosphericpressure. After a short interval of time, valve 22 1s closed and theapparatus is fully conditioned to receive the air that has beenpreviously introduced into container I. The size of the expansionbottles to be used is dependent upon the size of core conpressure incontainer I is measured by pressure gauge 1 or in any other manner wellknown in the art. Air at a known superatmospheric pressure is admittedinto core container I and valves 9 and 5 are then closed, trapping theair within core container I. Before expanding and measuring the airentrapped in the core container, it is necessary to condition that partof the apparatus in which expansion is to take place. This isaccomplished by opening valves 22, 2|, I9 and I8, subjecting manifold20, calibrated burette I8, mercury manometer I1 and water manometer I5to atmospheric pressure. In the step outlined in the preceding sentence,3-way valve I9 is open to connect burette I8 to the system. Valves 23,

32, 33, 34, 35 and 38 remain; closed during this operation. Valves I8,I9, 2i and 22 are then closed. Valve I9 is next opened to the atmosphereand mercury from leveling bulb 31 15 adtainer I and the size of coresection 44 to be tested. Assume that bottle 21 is' of suitable size tohold part of the air to be expanded from core container I. Valve 32 isthen opened and valve 8 slightly opened, allowing the air to expand fromcontainer I into bottle 21. The pressure on mercury manometer 24 andpressure gauge 1 is observed at all times and if appreciable pressurestill exists within container I after expansion into bottle 21, valve 33is opened and the air is allowed to further expand to bottle 28. If

the indicated pressure on gauge 1 is now almost atmospheric, but aslightly elevated pressure still exists within the system, as'shown onmanometer 24, valve I9 is opened, connecting burette I8 into the system.By lowering mercury leveling bulb 31 and opening valve 39 a smallamount, the pressure within the system can be reduced to approximatelythat of the atmosphere. At this time, valve I6 is openedand watermanometer I5 1 is connected into the system. This manometer willindicate a very slight diflerential between the pressure within theapparatus and that of the atmosphere. Further adjustment of the heightof the mercury column in burette I8 will make the pressure within theapparatus equal to that of the atmosphere.

The volume of air that had been admitted into core container I atsuperatmospheric pressure, designated as P5, is equivalent to theinternal volume of bottles 21 and 28 plus the volume of air in buretteI8, after expansion to atmospheric pressure, designated as Pa. Atsuperatmospheric pressure, this volume of air represented the differencebetween the internal volume of the empty core container plus the volumeof the appurtenances and Vn. The air admitted into the core containerunder pressure is expanded for convenience in measuring, and its volumeat atmospheric pressure may then be designated as V2.

It is essential to my calculations to know the volume of air atatmospheric pressure, designated as Vi, that can be placed in thecontainer I and the appurtenances at the aforementioned superatmosphericpressure with the core 44 removed from the container. The differencebetween V1 and V2 represents the volume of nonporous mareads at- SearchRoon terials of the core and the nonconnected pore spaces; or I maywrite mathematically I) ejonv2) v.

V! may also be determined by following the procedure outlined withrespect to determine V2, if desired.

In the foregoing calculations and measurements, necessary correctionsmust be made for indicating means connected to the receptacle, deviationfrom the ideal gas laws and for changes means for transmitting gas intothe receptacle in temperature and pressure. at a known pressure abovesaid predetermined From the foregoing, it is believed that the pressure,gas receiving means of variable volumethod and apparatus for practicingmy instant metric capacity connected to the receptacle, and inventionwill be readily comprehended by per- 15 means associated with the gasreceiving means sons skilled in the art. It is to be clearly underandcontrolling the pressure within the gas restood. however, that variouschanges in the apceiving means without loss of gas transmitted paratusherewith shown and described as a prethereinto. fer ed E b iment f yinvention and in the 5. In apparatus for determining the volume of modesof operation outlined above may be re- 20 connected pore spaces in aporous body, the comsortcd to w t departing from e pirit Of binationcomprising a receptacle for containing the invention as defined by theappended claims. the body at atmospheric pressure, pressure indi- Iclaim: eating means connected to the receptacle, means 1. In a method ofdetermining the volume of for transmitting gas into the receptacle at aconnected pore spaces in a porous body, he S ps :5 knownsuperatmospheric pressure, gas receiving comprising placing the body ina closed zone at a means of variable volumetric capacity connected kn wnp e, introducing gas at a predeterto the receptacle, and means forlowering the mined Pressure that is above said known pressure pressurewithin the gas receiving means to a point into the closed zone, placingthe closed zone in below atmospheric pressure. communication with asecond closed zone which :m 6. In apparatus for determining theeffective is at a pressure below said known pressure, exporosity of aporous body, the combination companding the gas from the first closedzone into prising a receptacle for containing the body at a the secondclosed zone until the pressure in both predetermined pressure, pressureindicating zones is substantially that of the above menmeans connectedto the receptacle, means for tioned known pressure, and thereuponascertain- 35 transmitting gas into the receptacle at a known ing thevolume occupied by the gas in the second pressure above saidpredetermined pressure, a zone. manifold connected to the receptacle,gas receiv- 2. In a method of determining the volume of ing means ofvariable volumetric capacity conconnected pore spaces in a porous body,the steps nected to the manifold, and means for lowering comprisingplacing the body in a closed zone at 40 the pressure within the gasreceiving means to a atmospheric pressure, introducing gas at knownsuperatmospheric pressure into the closed zone, placing the closed zonein communication with a second closed zone which is at a pressure belowatmospheric pressure, expanding the gas from the first closed zone intothe second closed zone until the pressure in both zones is substantiallyatmospheric, and thereupon ascertaining the volume occupied by the gasin the second zone.

3. In a method of determining the effective porosity of a formationcore, the steps comprising placing the core in a closed zone atatmospheric pressure, introducing dry gas at known superatmosphericpressure into the closed zone, placing the closed zone in communicationwith a second closed zone which is substantially evacpoint belowatmospheric pressure.

'7. In apparatus for determining the effective porosity of a formationcore, the combination comprising a receptacle for containing the core atatmospheric pressure, pressur indicating means connected to thereceptacle, means for transmitting substantially dry gas into thereceptacle at a known superatmospherie pressure, a manifold connected tothe receptacle, gas receiving means connected to the manifold andincluding a plurality of containers of predetermined volumetric capacityand valve means for selectively placing the container in communicationwith the manifold, and mean for substantially evacuating the containers.

ELMER O. MATTOCKS.

CERTIFICATE OF CORRECTION. Patent No. 2,525,556. July 6', 19m.

ELMER 0 HAT'I'OCKS It is herebycertified that error appears in theprinted specification of the above mgmb ered patent requiring correctionas follows: Page 5, first column, line ii, in the formula, for

read s s and that the said Letters Patent shonld be read with thiscorrection therein that the same may conform to the record of the cesein the Patent Office.

Signed and sealed this 26th day of October, A. D. 1915.

- i Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

